U.S. patent application number 14/297817 was filed with the patent office on 2014-12-11 for bicycle transmission.
The applicant listed for this patent is Robert William Thompson. Invention is credited to Robert William Thompson.
Application Number | 20140361511 14/297817 |
Document ID | / |
Family ID | 48805842 |
Filed Date | 2014-12-11 |
United States Patent
Application |
20140361511 |
Kind Code |
A1 |
Thompson; Robert William |
December 11, 2014 |
BICYCLE TRANSMISSION
Abstract
A chainless drive mechanism for a bicycle using pedal arms, one
on each side of the bicycle, each pedal arm carrying a pedal
engageable with a rider's foot. Each pedal arm is mounted to a
crank by a rotating joint and connected to the frame of the bicycle
by a link, each link having rotating joints at each end. The cranks
are connected by a shaft passing through the hub of to the driven
wheel of the bicycle. The cranks may be connected to the driven
wheel by a multi ratio free wheeling gear mechanism.
Inventors: |
Thompson; Robert William;
(Camberley, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Thompson; Robert William |
Camberley |
|
GB |
|
|
Family ID: |
48805842 |
Appl. No.: |
14/297817 |
Filed: |
June 6, 2014 |
Current U.S.
Class: |
280/262 |
Current CPC
Class: |
B62M 1/30 20130101; B62M
1/26 20130101; B62M 1/38 20130101; B62M 3/083 20130101; B62M 1/36
20130101; B62M 11/18 20130101 |
Class at
Publication: |
280/262 |
International
Class: |
B62M 1/36 20060101
B62M001/36 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2013 |
GB |
GB1310092.0 |
Claims
1. A chainless drive mechanism for a bicycle having: a frame; a
front steering wheel; and a rear non-steering wheel; the chainless
drive mechanism having two pedal arms, one said pedal arm
positioned in use on each side of the bicycle, each said pedal arm
having a pedal connected thereto at the forward end thereof, said
pedals connected to the pedal arms by rotating joints, each said
pedal arm being mounted to a crank by a respective rotating joint,
the rearward end of each said pedal arm being connected to the
frame of the bicycle by a respective link, each said link having a
respective rotating joint at each end, said cranks being rotatable
and connected by a shaft through the hub of and in drivable
communication with the rear non steering wheel of the bicycle, each
pedal arm having a geometry where the center of the rotating joint
connecting the link to the pedal arm is below a straight line
between the center of rotation of the joint connecting the pedal to
the pedal arm and the center of rotation of the joint connecting
the pedal arm to the crank.
2. A chainless drive mechanism for a bicycle according to claim 1,
wherein the pedal arms are triangular frames.
3. A chainless drive mechanism for a bicycle according to claim 1,
wherein the length of the links are adjustable.
4. A chainless drive mechanism for a bicycle according to claim 1,
wherein the rotating joints at one or both ends of each said link
are a combination of self-aligning and low friction rolling element
bearings.
5. A chainless drive mechanism for a bicycle according to claim 1,
wherein the cranks are connected to a wheel of the bicycle by a
gear mechanism.
6. A chainless drive mechanism for a bicycle according to claim 5,
in which the gear mechanism comprises a plurality of epicyclical
gear stages, each said epicyclical gear stage having a sun gear a
plant gear, a carrier and a ring gear and an input to the carrier,
output from the ring gear and the sun gear being selectively
connectable to the frame of the bicycle and each said epicyclical
gear stage being fitted with a one way clutch mechanism.
7. A chainless drive mechanism for a bicycle according to claim 6,
in which the one way clutch mechanism is a pawl mounted on, and
pivoting on, the carrier, said pawl acted on by a spring and
engageable with the gear teeth of the ring gear,
8. A chainless drive mechanism for a bicycle according to claim 6
in which the gear mechanism uses a plurality of epicyclical gear
stages of a first ratio and a plurality of epicyclical gear stages
of a second ratio where the second ratio is substantially equal to
the first ratio raised to the power of one and a half.
9. A chainless drive mechanism for a bicycle according to claim 6,
in which the gear stages are connected in series.
10. A chainless drive mechanism for a bicycle according to claim 6,
wherein each sun gear is selectively connectable to the frame of
the bicycle using a controllable pawl acting on a ratchet, the pawl
being controlled by a pin substantially parallel to the gear hub
axis, one end of the pin engaged with the pawl a second position on
the pin engaged with the frame of the bicycle and a third position
on the pin engaged with a notched control member, a spring acting
on the pin or pawl to urge the pawl into contact with the
ratchet.
11. A chainless drive mechanism for a bicycle according to claim 6,
in which a thrust ring is fixed to the outer face of a ring gear,
said thrust ring contacting the outer face of the planet gear,
12. A chainless drive mechanism for a bicycle according to claim 5,
where the gear mechanism is a lay shaft gearbox.
13. A chainless drive mechanism for a bicycle according to claim 5,
wherein the gear mechanism is a lay shaft gearbox having a
plurality of secondary shafts, the gears on the secondary shafts
being selectively coupleable.
14. A chainless drive mechanism for a bicycle according to claim 5,
wherein the gear mechanism is an epicyclical gear mechanism.
15. A chainless drive mechanism for a bicycle according to claim 1,
incorporating a brake.
16. A bicycle comprising the drive mechanism of claim 1.
17. A bicycle as claimed in claim 16, having clips or attachments
whereby the riders feet are securely coupled to the pedals in
use.
18. A bicycle as claimed in claim 16, wherein the pedal arm length
places the pedals substantially below the saddle of the
bicycle.
19. A bicycle as claimed in claim 16, wherein the bicycle is
adapted to be folded.
20. A bicycle as claimed in claim 16, wherein, wherein the bicycle
further comprises a suspension.
21. A gear mechanism for a drive mechanism for a bicycle, wherein,
the gear mechanism comprises a plurality of epicyclical gear
stages, each said epicyclical gear stage having a sun gear a plant
gear, a carrier and a ring gear and an input to the carrier, output
from the ring gear and the sun gear being selectively connectable
to the frame of the bicycle and each said epicyclical gear stage
being fitted with a one way clutch mechanism.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of patent application
GB1310092.0 entitled Bicycle Transmission and filed on Jun. 6,
2013; of which the entirety is incorporated herein by
reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a drive mechanism/transmission
mechanism for a bicycle.
[0004] 2. Background
[0005] Bicycles commonly use roller chain transmissions, with
multiple chain wheels and sprockets together with derailleur
shifting mechanisms, to connect the pedals to a wheel. Roller
chains wear and stretch in use and the sprockets, with which they
engage, wear until they break, slip or otherwise fail, requiring
expensive replacement. To minimize wear the mechanism needs regular
cleaning and lubrication. This is especially the case for bicycles
used off-road where contamination by abrasive matter is
unavoidable. Roller chain mechanisms also suffer from a number of
other problems, for example, the chain can contaminate and snag the
rider's clothing, the chain can become dislodged from the
sprockets, shifting cannot readily take place when stationary and
the shifting mechanism itself is prone to contamination and
vulnerable to damage. Also the externally lubricated chain of a
folding bicycle is likely to contaminate the user's clothing when
the folded bicycle is carried.
[0006] The large pitch of roller chains, and the resulting small
number of teeth on each sprocket, results in inconsistent ratio
changes. This gives an inconsistent feel to shifting and requires a
greater number of sprockets to be used to cover a given range of
ratios while maintaining close ratio shifts.
[0007] The crank shaft carrying the pedals of a roller chain
transmission bicycle must be mounted on the frame of the bicycle in
front of the rear wheel so as not to interfere with the wheel's
rotation. This, combined with the circular motion of the pedals,
results in a pedaling action where the downward portion of motion
of the pedal is short in comparison with the full motion, and
occurs some distance in front of the rider's center of mass. Roller
chain transmission bicycles with a short wheel base, as used in
racing, suffer from toe overlap, where the rider's feet can
interfere with the front wheel when steering.
[0008] Bicycles often incorporate suspension systems to improve
riding on rough terrain. For a roller chain bicycle, the pivot
point for the rear suspension on the frame must be substantially at
the center of the crank shaft, to minimize variations in the center
distance between the chain wheel on the crank shaft, and the
sprockets on the rear wheel, as the suspension operates. The need
to co-locate the crank shaft and suspension pivot mounting points,
both of which require high strength and stiffness, can result in
additional complexity, cost and weight.
[0009] Early bicycles, generally predating roller chain bicycles,
used a variety of treadle mechanisms. One example used a pair of
levers mounted on cranks connected to the steering, front, wheel
with a link to the forks at their forward ends and a pedal at their
rear ends. This mechanism does not have the same disadvantages as a
roller chain transmission, but has a number of other disadvantages.
This bicycle had no gearing, with the driven wheel rotating at the
same frequency as the pedals thus limiting speed for a given wheel
size. This bicycle did not have a free wheel mechanism so the rider
was unable to rest his legs when moving, and it was not possible to
set the position of a pedal to assist starting to ride. As the
pedal and drive mechanism was mounted to the front wheel, forces
from the rider's legs would interfere with the steering of the
bicycle.
[0010] It is an object of the present invention to address the
above problems.
SUMMARY OF THE INVENTION
[0011] In a main aspect of the present invention by using zero
maintenance pedal arms and links connected to cranks protruding
from a multi ratio gear and free wheel mechanism coupled to the
rear driving wheel of the bicycle, the pedal arms having a geometry
giving forward pedaling bias for a comfortable, practical and
improved pedaling action.
[0012] According to the present invention there is provided a
chainless drive mechanism for a bicycle having a frame and front
steering wheel and rear non-steering wheel, the chainless drive
mechanism having two pedal arms, one said pedal arm positioned in
use on each side of the bicycle, each said pedal arm having a pedal
connected thereto at the forward end thereof, said pedals connected
to the pedal arms by rotating joints, each said pedal arm being
mounted to a crank by a respective rotating joint, the rearward end
of each said pedal arm being connected to the frame of the bicycle
by a respective link, each said link having a respective rotating
joint at each end, said cranks being rotatable and connected by a
shaft through the hub of and in drivable communication with the
rear non steering wheel of the bicycle, each pedal arm having a
geometry where the center of the rotating joint connecting the link
to the pedal arm is below a straight line between the center of
rotation of the joint connecting the pedal to the pedal arm and the
center of rotation of the joint connecting the pedal arm to the
crank.
ADVANTAGES
[0013] The bicycle transmission mechanism suitably uses only rotary
joints which can readily be sealed to retain lubricant and keep out
contamination, providing a high efficiency zero maintenance
mechanism. The pedal arms require no external lubrication and only
reciprocate adjacent to the rider's legs and therefore will not
snag or soil the riders clothing. The absence of externally
lubricated components is a particular advantage to a bicycle
designed to be folded and carried.
[0014] The geometry of the pedal arms, cranks and links results in
a forward pedaling bias providing a comfortable and efficient
pedaling action which is practical to use with a free wheel
mechanism. The pedal arm mechanisms, being mounted from the frame
adjacent to the rear wheel, allow rear suspension to be readily
incorporated, using a simple pivoting joint, forward of the rear
wheel, on the frame of the bicycle.
[0015] Preferably the cranks are connected to the wheel of the
bicycle by a multi ratio gear and free wheel mechanism allowing
comfortable and efficient riding over a range of riding
conditions.
[0016] Preferably the multi ratio gear mechanism is fitted within
the wheel hub of the bicycle and is sealed to retain lubricant and
keep out contamination, so minimizing wear and eliminating the need
for maintenance.
[0017] Preferably the multi ratio gear mechanism uses a number of
epicyclical gear stages connected in series, the input to each
stage at the carrier and the output at the ring gear, providing
high efficiency, the ratios of the stages configured to give
consistent ratio changes on shifting, to provide a consistent feel
to the rider, and to cover the required range of ratios with a
minimum number of ratios while maintaining close ratio shifts.
[0018] Preferably the gear ratios are selected by controllable
pawls acting on ratchet wheels to selectively lock the sun gears of
the epicyclical gear stages allowing shifting when the bicycle is
stationary as well as when moving.
[0019] Preferably the length of the link connecting the pedal arm
to the frame of the bicycle is readily adjustable to raise or lower
the height of the pedals to suit the preference of the rider.
[0020] Preferably the length of the pedal arms places the pedals
substantially below the saddle of the bicycle, providing an
improved pedaling action where the rider can apply their full
weight on the pedals, using articulation of the knee joint as well
as of the hip joint, on the downward stroke, from a seated
position. This pedal arm geometry positions the rider's feet away
from the front wheel of the bicycle, avoiding toe overlap, even
with a short wheel base.
[0021] The summary of the invention is provided as a general
introduction to some of the embodiments of the invention, and is
not intended to be limiting. Additional example embodiments
including variations and alternative configurations of the
invention are provided herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The accompanying drawings are included to provide a further
understanding of the invention and are incorporated in and
constitute a part of specification, illustrate embodiments of the
invention, and together with the description serve to explain the
principles of the invention.
[0023] FIG. 1 shows an example of prior art showing the drive
mechanism referred to as American Levers used on a bicycle known as
an American Safety bicycle.
[0024] A preferred embodiment of the present invention will now be
more particularly described by way of example only and with
reference to FIGS. 2 to 7 of the accompanying drawings.
[0025] FIG. 2 shows a bicycle with pedal arm geometry embodying the
present invention.
[0026] FIG. 3 shows diagrammatically the gear configuration for the
preferred embodiment of the gear mechanism of the present
invention.
[0027] FIG. 4 shows a plan view and two section views of the
preferred shifting components of the gear mechanism.
[0028] FIGS. 5, 6 and 7 are a perspective view, right side view and
front elevation view of the bicycle corresponding to FIG. 2 and
showing the right and left side pedals at slightly different
positions of turning as in use and showing in greater detail the
connection of the pedal arm to the crank and to the link.
[0029] Corresponding reference characters indicate corresponding
parts throughout the several views of the figures. The figures
represent an illustration of some of the embodiments of the present
invention and are not to be construed as limiting the scope of the
invention in any manner. Further, the figures are not necessarily
to scale, some features may be exaggerated to show details of
particular components. Therefore, specific structural and
functional details disclosed herein are not to be interpreted as
limiting, but merely as a representative basis for teaching one
skilled in the art to variously employ the present invention.
[0030] As used herein, the terms "comprises," "comprising,"
"includes," "including," "has," "having" or any other variation
thereof, are intended to cover a non-exclusive inclusion. For
example, a process, method, article, or apparatus that comprises a
list of elements is not necessarily limited to only those elements
but may include other elements not expressly listed or inherent to
such process, method, article, or apparatus. Also, use of "a" or
"an" are employed to describe elements and components described
herein. This is done merely for convenience and to give a general
sense of the scope of the invention. This description should be
read to include one or at least one and the singular also includes
the plural unless it is obvious that it is meant otherwise.
[0031] Certain exemplary embodiments of the present invention are
described herein and illustrated in the accompanying figures. The
embodiments described are only for purposes of illustrating the
present invention and should not be interpreted as limiting the
scope of the invention. Other embodiments of the invention, and
certain modifications, combinations and improvements of the
described embodiments, will occur to those skilled in the art and
all such alternate embodiments, combinations, modifications,
improvements are within the scope of the present invention.
DETAILED DESCRIPTION OF THE ILLUSTRATED PRIOR ART
[0032] FIG. 1 shows the lever, link and crank mechanism, known as
American Levers, from an example of prior art known as an American
Safety bicycle, as described and illustrated in "Sturmey's
Indispensable Handbook to the Safety Bicycle by Henry Sturmey,
first published 1885. For clarity the mechanism from one side only
of the bicycle is shown. A pedal 1 on which the rider pushes with a
foot is mounted on the lower rear end of a lever 7. The lever is
connected to the forks 2 of the bicycle by a link 3, the link
having rotating joints at each end. The lever is connected to a
crank 4, the crank being connected to the axle 6 mounted on
rotating joints on the forks 2 of the bicycle and connected to the
wheel.
[0033] This bicycle used a pair of cranks at 180 degrees
displacement from each other, with one crank on each end of the
axle through, and connected to, the front wheel, and two lever,
pedal and link mechanisms, one on each side.
[0034] The purpose of this mechanism was to move the pedals towards
the rear of the bicycle, compared to pedals mounted directly to the
cranks, thereby allowing a riding position further behind the
center of the front wheel, and therefore improving the stability
and safety of the bicycle. As the bicycle moves forward, and the
wheel and cranks rotate, the levers move up and down being attached
to the cranks, and the pedals, with which the rider's feet engage,
move in approximately elliptical paths. The rider causes the cranks
to rotate, and so propels the bicycle by pushing the pedals in time
with the motion As no free wheel mechanism is used the pedals are
driven past the upper and lower points of travel by the forward
momentum of the bicycle.
[0035] This bicycle has the disadvantage of having no gearing, with
the driven wheel rotating at the same frequency as the pedals, so
limiting speed for a given wheel size since the rate, often
referred to as cadence, at which pedals can be operated efficiently
by the rider's legs, is limited. This bicycle also has the pedal
and drive mechanism mounted to the front wheel. While pedaling,
forces from the rider's legs would therefore interfere with the
steering of the bicycle, since the rider is seated on the frame of
the bicycle but the pedals and drive mechanism are mounted on the
forks. The front steering wheel must pivot relative to the frame
and the rider's seat to steer, so the rider's legs will restrict
steering movement. Also forces from the rider's legs will tend to
steer the front wheel so requiring a reaction force to be applied
at the handle bars by the rider's arms. This interaction between
pedaling and steering therefore reduces stability and increases the
skill and effort required to ride the bicycle.
[0036] This bicycle also had the disadvantage of not having a free
wheel mechanism to allow a rider to rest their legs stationary on
the pedals while the bicycle continues moving, for example on a
decent. To commence riding on a bicycle with a free wheel mechanism
the rider will often first set one pedal in a position at the start
of a forward driving stroke. This is done by rotating the pedal
backwards, allowed by the free wheel mechanism, to a suitable
starting position using one foot while standing on the other foot.
Forward motion can then be initiated by a combination of pushing
off from the ground with one foot while starting to pedal forward
with the other foot engaged with the set pedal. This gives the
rider time to put the second foot on to the pedal and then continue
pedaling before the bicycle slows to a point where balance is lost.
In the case of this prior art bicycle, setting of the pedal in a
starting position without rolling the bicycle forwards or
backwards, which could be dangerous or impractical, especially when
at a road junction, is not possible, as no free wheel mechanism is
employed.
[0037] The lever and link mechanism of this prior art bicycle does
not suffer from some of the disadvantages of a roller chain drive
mechanism. The rotary joints of the mechanism can be readily sealed
to retain lubricant and exclude contaminants. Use of this type of
mechanism connected to the rear non steering wheel of a bicycle and
incorporating a free wheel, multiple gear ratio mechanism therefore
gives the possibility of overcoming the disadvantages of the roller
chain drive. However, simple reversal of the mechanism from the
prior art using a long link reaching upward and forward to the
frame of the bicycle from the rear of the lever does not result in
a practical mechanism. This arrangement results in a geometry where
the highest point of travel of the pedal on one side of the bicycle
occurs after the lowest point of travel on the other pedal. This
makes pedaling forward impractical when a free wheel mechanism is
used, especially when standing on the pedals, where the rider's
weight on the lower pedal holds it at the lowest point and stops
the higher pedal passing it's highest point. Some modification to
the geometry of the mechanism is therefore required to provide
practical and effective solution which can be used with a free
wheel mechanism.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0038] FIG. 2 shows a preferred embodiment of bicycle with the
pedal arm and link geometry of the present invention. For clarity
the mechanism from one side only of the bicycle is shown. A pedal 1
is mounted by a rotating joint to the forward end of a rigid pedal
arm 7. The pedal arm is mounted by a rotating joint to a crank 4.
The crank rotates around a crankshaft 6 which is mounted by a
rotating joint to the frame 5. The pedal arm 7 is further connected
to the frame by a link 3, the link having rotating joints at each
end. It should be noted that the geometry of the pedal arm 7, has
the connection to the link behind the connection to the crank and
below a straight line, indicated by a dashed line in FIG. 2,
through the pedal mounting position and the crank mounting
position. This geometry requires the link to be substantially
vertical to maintain reasonable angles between the link, to
minimize forces in the link and the arm and to avoid the link
crossing the center of the crank, and so a rearward extension to
the frame of the bicycle is required to provide the connection
point of the link to the frame. This particular geometry results in
a forward pedaling bias with the highest point of travel of one
pedal occurring before the lowest point of travel of the other
pedal. When pedaling, therefore, as the rider's foot on one side of
the bicycle reaches it's lowest point, the other pedal and foot has
already started it's downward stroke, allowing a smooth
continuation of the pedaling action, even if a free wheel mechanism
is employed. This forward pedaling bias is particularly important
when the rider is standing on the pedals where the rider's weight
forces the pedal to stop at the lowest point as pedal pressure is
transitioned to the opposite pedal.
[0039] It should be noted that with this preferred pedal arm
geometry, the three mounting points on the arm for the rotary
joints for the pedal, crank and link, form a triangle. The pedal
arm therefore can be made as a triangular frame so providing high
strength and stiffness.
[0040] The bicycle transmission mechanism according to the present
invention uses a pair of cranks at 180 degrees displacement from
each other with one crank on each end of the axle through, and
connected to, the rear wheel, and two pedal arm and link
mechanisms, one on each side.
[0041] It should be noted that in the preferred embodiment of the
invention, the rotating joints used at each end of the link
incorporate ball or spherical joints to allow for small
misalignments in the mechanism due to manufacturing tolerance and
the flexibility of the components under loads. Additionally, to
maximize the efficiency of the mechanism, a low friction rolling
element bearing, for example, a needle roller bearing is also
incorporated into the joint. Self-aligning rolling element
bearings, for example spherical roller bearings, could be used,
however these tend only to be available in larger sizes which would
add unnecessarily to the weight of the assembly.
[0042] Since the pedal arm is mounted on the crank, as the crank
rotates it moves horizontally as well as vertically. The pedal
therefore follows a path forming an open loop. It is thus possible
for the rider to control the movement of the pedal past the
extremes of movement making the use of a free wheel mechanism
practical. This allows the rider to set the pedal into a starting
position, in the same manner as when using a bicycle using a roller
chain transmission and having a circular pedal motion.
[0043] For a bicycle using a roller chain drive mechanism the crank
shaft carrying the cranks must be positioned some distance in front
of the rear wheel of the bicycle so that the crank shaft, its
bearings and the frame which supports it, do not interfere with the
rotation of the rear wheel. This positions the crank shaft in front
of the saddle. This combined with the length of the crank puts, the
portion of the motion which is substantially vertically downward,
which is small in comparison with the full travel, some distance in
front of the saddle. When seated on the saddle, therefore, it is
difficult for the rider to apply full downward force on the pedal
since his or her weight is centered some distance behind the
downward portion of motion of the pedal. The most efficient use of
the rider's body is when the legs push vertically downwards
reacting against the rider's weight, as this does not require any
additional muscle action, for example by the arms through the
handle bars, to react force on the pedals. Also in the downward
portion of the movement of the pedal, the knee joint articulation
is minimal. The muscles of the leg used to extend the knee joint
are therefore poorly utilized. Knee joint articulation occurs
mainly as the pedal travels over the top of its circular path. To
make use of the knee extension muscles, therefore, requires force
to be applied to the pedal in a forward rather than a downward
direction and is therefore more difficult and additionally requires
the use of toe clips or other devices to couple the rider's feet to
the pedals.
[0044] Due to these limitations of the rotary motion of the pedals
and the forward position of the crank shaft, in difficult riding
conditions, for example, when riding up a steep slope or when
accelerating, the rider of a roller chain bicycle will tend to rise
off the seat and shift his or her weight forward vertically above
the downward portion of the motion of the pedals. In this stance,
full use of both the knee extension muscles and the hip joint
extension muscles can be made. This stance, where the rider's
weight is supported by the legs, is, however, tiring, and so is
only generally used for short periods.
[0045] It should be noted that in the preferred embodiment of the
present invention the pedal arm length is chosen to place the
pedals substantially below the saddle of the bicycle, which is
possible since the crank shaft passes through the wheel hub and the
pedal arms carry the pedals adjacent to the wheel without
interfering with its motion. Also, the length of the pedal arm, in
combination with the length of the crank, means the motion of the
pedal is substantially vertically up and down in a narrow loop.
This preferred geometry provides an improved pedaling action where
the rider can apply their full weight on the pedals, using
articulation of the knee joint as well as of the hip joint, on the
downward stroke while remaining in the seated position.
Additionally it should be noted that due to the more linear motion
of the pedals, compared to a roller chain drive mechanism using
rotary pedal motion, a greater proportion of the travel of the
pedal is in a near vertical sense and so more useful work is
performed by the legs with force applied vertically downward
reacting against the rider's weight. As a greater portion of the
travel of the pedal is in a vertical sense a shorter overall stroke
can be used allowing for more effort to be performed when the legs
are close to full extension.
[0046] This preferred pedal arm geometry, placing the rider's feet
substantially below the saddle, makes the forward most point of
travel of the rider's feet substantially further away from the
front wheel of the bicycle compared to a roller chain bicycle. A
short wheel base bicycle is therefore possible without crossover,
and so avoids the possibility of the rider's feet contacting the
front wheel when steering, which could causing a fall.
[0047] It should be noted that a pedal arm transmission according
to the present invention is suitable for use with or without toe
clips. The use of toe clips or other devices which securely couple
the rider's feet to the pedals has similar advantages as when used
with a roller chain type transmission. The rider can exert
considerably greater useful force on the drive mechanism by both a
pulling action on the upward moving pedal at the same time as
downward force on the other pedal. Since the pedals move in near
vertical narrow loops, the vertical force from pulling up on one
pedal can be reacted vertically down on the other pedal, resulting
in useful work at both pedals with minimal additional reaction
forces and minimal additional muscle effort being required.
[0048] It should be noted that a bicycle frame, for use with a
pedal arm transmission according to the present invention, can
readily be designed to incorporate suspension. Front suspension can
be incorporated by the use of telescopic forks or other devices
mounting the front wheel, as for a roller chain bicycle. For rear
suspension, the frame can readily incorporate a pivot and a spring
and damper unit to allow the rear wheel to move up and down
relative to the saddle and forward section of the frame. The pivot
can readily be positioned in front of the rear wheel and below the
saddle since the transmission components are all mounted away from
this area on the frame adjacent to the rear wheel. The joint, and
the part of the frame connecting to it, can readily fit between the
two pedal arms, and close to the position of the pedals. The pedals
and seat of the bicycle, which support the rider, therefore move
substantially in unison as the suspension operates, decoupling the
rider from the vertical movement of the rear wheel.
[0049] It should be noted that a pedal arm transmission according
to the present invention may incorporate a device to readily allow
the adjustment of the length of the link. This allows for the
convenient adjustment of the height of the pedals relative to the
frame of the bicycle to cater for different rider proportions and
preferences as well as varying riding conditions. This adjustment
mechanism may take the form of a screw thread and suitable locking
device. For a roller chain transmission bicycle, the height of the
pedals cannot readily be changed as the center of rotation of the
pedals is a fixed part of the frame of the bicycle. This adjustment
of the height of the pedals can be used in conjunction with the use
of cranks of different length to provide for varying pedal stoke
length, without compromising pedal height, as would be the case on
a conventional roller chain bicycle.
[0050] FIG. 3 shows, diagrammatically, the gear configuration for
the preferred embodiment of the gear mechanism. The two pedal arms
7, 7a are shown on each side of the diagram in plan view carrying
pedals 1, 1a and connected to the frame 5 by links 3, 3a. Cranks 4,
4a are connected by the crank shaft 6 which passes through the
central axis of the gear hub assembly.
[0051] The gear hub assembly in this preferred embodiment of the
present invention uses four epicyclical gear stages, 8, 8a, 9, 9a,
Each of these epicyclical gear stages is configured to have the
input to the planet carrier, the output from the ring gear, and the
sun gear selectively connectable to the frame of the bicycle. This
configuration of epicyclical gears gives a speed increase with the
output from the ring gear rotating at a higher speed and in the
same sense as the carrier when the sun gear is stationary. This
configuration of epicyclical gearing provides the highest possible
efficiency power transfer since the input and the output rotate in
the same direction so the relative speed between the gear elements
is low and therefore mesh loss is correspondingly low. The four
epicyclical gear stages are connected in series. Planet carrier 16
is the input to the gear hub and is connected to the crank shaft 6
in the middle of the hub assembly. The ring gear 13 of this first
stage 9 is connected to the planet carrier 17 of the second stage
8. The ring gear 10 of the second stage 8 is connected to the
carrier 16a of the third stage 9a. The ring gear 13a of the third
stage 9a is connected to the planet carrier 17a of the fourth stage
8a. The ring gear of the fourth stage 8a is connected to the hub
case 18, which is connected to the wheel rim and tire of the
bicycle.
[0052] Preferably axial location of each epicyclical gear stage is
controlled by thrust rings, not drawn, fixed to either side of each
ring gear which contact the outer edges of the planet gears,
[0053] Each epicyclical gear stage has a one way clutch mechanism
19 between the carrier and the ring gear. In the case of this
preferred embodiment of the present invention, the one way clutch
mechanism takes the from of a spring loaded pawl, pivoting in the
carrier, which engages with the teeth of the ring gear in one sense
of relative rotation of the ring gear and carrier, and lifts out of
engagement under the opposite sense of relative rotation of the
ring and carrier. If the sun gear of a stage is not locked, and is
free to rotate, then the sun will rotate forward with the carrier,
the one way clutch mechanism will lock, and the ring will be driven
at the same speed as the carrier. With the sun gear released,
therefore, the stage is locked, and drives from input to output
without speed increase, and without relative rotation of the gears,
so minimizing frictional loss.
[0054] It should be noted that within the scope of the present
invention a one way clutch mechanism may be used to act between any
two of the elements of the epicyclical gear stage, so to lock the
stage and provide a connection from input to output, without a
ratio change, when the sun gear is not connected to the frame of
the bicycle. Also it should be noted that a ratchet wheel or ring
may be used attached to one of the elements on which a pawl or
other catch may act to provide a one way clutch mechanism. Other
one way clutch mechanisms will no doubt be known to one skilled in
the art which could be employed between elements of the epicyclical
stage to achieve the desired function according the present
invention for example a sprag clutch or a roller clutch.
[0055] Each of the four sun gears is selectively connectable to the
frame of the bicycle by a controllable pawl 20 which engages with
ratchet teeth inside the bore of each of the larger sun gears 12,
12a and on the inside of rings 21 and 21a connected to the two
smaller sun gears 15, 15a.
[0056] It should be noted that, for reasons of clarity, bearings
have not been included in the diagram. It should also be noted that
each of the bearings on the outside of the gear hub, for example
between the hub and the frame of the bicycle or between the crank
shaft and the frame of the bicycle, are readily sealed and
therefore the hub assembly in the preferred embodiment of the
invention will be sealed. A volume of lubricant can therefore be
retained within the hub to continually lubricate all the
components, to protect from wear and minimize friction, so
maximizing efficiency. The sealing of the hub also prevents ingress
of contaminants, for example water or grit, which would otherwise
cause rapid wear of the components of the hub. Regular maintenance,
therefore, is not required.
[0057] FIG. 4 shows a diagrammatical plan section view of the gear
selection components of the preferred embodiment of the present
invention, being a portion of FIG. 3, and two further section side
views to illustrate the function thereof.
[0058] The pawls 20 and 20a are controlled by pins 22 and 23 which
are substantially parallel with the axis of the gear hub. These
pins pivot on ball ends located in the casing at their outboard
ends and engage with holes in the pawls at their inner ends. Pin 23
is longer than pin 22 so as to reach the pawl acting on the ring 21
mounted further inside the hub assembly. Small springs 27, 27a act
on the pins to push them outwards. The pins, therefore, will push
the pawls outward and into contact with the ratchet teeth 28 cut on
the inside of the sun gear 12. Alternatively, the spring may act on
the pawl to provide the same function. Similar teeth, not drawn,
are provided on the inside of the ring 21 for locking the smaller
sun gear 15. A shift control ring 24 is fitted around the two pins.
The ring has a series of notches 26 cut on its inside diameter. The
inside diameter of the ring is chosen so that when the ring is
rotated to a position where there is no notch in line with the pin,
the ring contacts the pin, holding it inwards, and so holding the
pawl inwards clear of the ratchet teeth, so allowing rotation of
the sun gear. If the ring 24 is rotated so that a notch is in line
with the pin, the pin can lift by action of the spring allowing the
pawl to contact the ratchet and lock the rotation of the sun gear.
In a non-preferred embodiment of the invention the pins may be
acted upon by control members with a pre-determined pattern of
notches, of a form other than a ring, for example a rod.
[0059] In this preferred embodiment of the present invention the
ring is rotated by a gear shift control cable connected to a handle
bar mounted indexing shifter as commonly used to control derailleur
gears. Other means of controlling the movement of the shift control
ring are possible and will no doubt be familiar to one skilled in
the art, for example by means of an electric servo motor or a
hydraulic actuator.
[0060] Two similar shift mechanisms are used, one on each side of
the hub. The two shift control cables 25, 25a are connected in
parallel to the same indexing shifter so that the two shift rings
24, 24a move in unison. A predetermined sequence of gear selections
can therefore be achieved by the design of the pattern of notches
cut on the inside of the shift control rings.
[0061] The lowest ratio achievable is with none of the gear stages
engaged. A 1:1 ratio is then provided with each stage locked by its
one way clutch mechanism, and the hub case and wheel then rotate at
the same speed as the cranks. No gears rotate so efficiency is
maximized.
[0062] If, when the bicycle is moving, the rider stops pedaling,
any of the one way clutches or pawl and ratchet rings in the gear
mechanism can operate to allow the input to remain stationary as
the bicycle continues to move forward. The gear configuration
therefore inherently has a free wheeling function.
[0063] The highest ratio achievable is with all four stages
engaged. Since the stages are connected in series the overall ratio
in this state is the multiple of the four individual ratios.
[0064] The preferred embodiment of the present invention uses two
epicyclical gear stages of one ratio and two of another ratio. The
two ratios are chosen to achieve a high number of different gear
ratios as well as substantially similar ratio changes between
consecutive gears for the majority of shifts. Using two stages of
one ratio and two of another also reduces the number of different
components used in the assembly. In this preferred embodiment of
the present invention the higher of the two ratios is substantially
equal to the lower ratio raised to the power of one and a half.
Combinations of the four stages can then provide a number of
consecutive gear ratios with a change in ratio being substantially
the square root of the lower of the stage ratios.
[0065] By way of example, in the preferred embodiment of the
present invention, the lower of the epicyclical gear stages uses 70
teeth for the ring gear 23 teeth for each planet gear and 23 teeth
for the sun gear, providing a ratio of approximately 1.329:1. The
higher of the epicyclical gear stages uses 70 teeth for the ring
gear, 16 teeth for each planet gear and 38 teeth for the sun gear,
providing a ratio of approximately 1.543:1.
[0066] The lowest ratio is 1:1 with no stages engaged. This ratio
is typical of the lowest gear used in bicycles designed for use off
road when climbing steep slopes. The second ratio is when one of
the lower ratio epicyclical stages is engaged and is 1.329:1. The
third ratio is with one of the higher stages engaged and is
1.543:1. The next ratio is with the two lower stages engaged and is
1.766:11. The next ratio is with one lower and one higher stage
engaged and is 2.051:1. The next ratio is with two higher gear
stages engaged and is 2.381:1. The next ratio is with two lower and
one higher stage engaged and is 2.725:1. The next ratio is with two
higher and one lower stage engaged and is 3.164:1. The highest
ratio is with all four stages engaged and is approximately 4.205:1
This highest ratio is suitable for high speed riding downhill.
[0067] The preferred embodiment of the invention therefore provides
nine distinct gear ratios from 1:1 to 4.205:1. The change in ratio
between the first and second ratio and between the eighth and ninth
ratio is 1.329. The change in ratio between each of the other gears
is approximately the square root of the lower stage ratio, which is
approximately 1.15, giving a 15% increase in ratio with each
shift.
[0068] Other choices of gear tooth numbers can be chosen to provide
wider or closer ratios as desired for different applications within
the scope of the present invention. Larger numbers of gear stages
may be employed to provide different ratios for other application
for example where a smaller wheel size is employed or where a
greater number of distinct ratios is required, within the scope of
the present invention. Smaller numbers of stages may be employed
for simplicity where a lower number of ratios are acceptable,
within the scope of the present invention.
[0069] For a bicycle requiring only one ratio a single epicyclical
gear stage may be used for example with the input to the carrier,
the ring gear fixed to the frame of the bicycle, and the output
from the sun gear.
[0070] For controlling the speed of the bicycle it is desirable to
use brakes which act to slow the wheels of the bicycle as demanded
by the rider. A brake can be included in the design of the gear hub
for example a brake disc may be mounted on the outside of the hub
and a corresponding brake caliper mounted to the frame of the
bicycle. Other forms of brake, as will no doubt be familiar to one
skilled in the art, may be included internally in the hub or acting
on the rims of the wheel. A brake fitted to the hub commonly
referred to as a coaster brake, which is operated by rotating the
pedals backward, could also be used.
[0071] It will no doubt be obvious to one skilled in the art that,
within the scope of the present invention, other possible gear
mechanisms can be used to connect the cranks to the wheel of the
bicycle, particularly if having a small number of different ratios
is acceptable. For example, simple lay shaft gear arrangements
mounted beside the wheel with the case fixed to the bicycle frame
could be used. Most conveniently this form of gearing would select
different ratios by selectively connecting the gears on the
secondary shaft using a free wheel clutch. A 1:1 ratio could be
provided by the inclusion of a free wheel mechanism between the
wheel and the crank shaft when no selection in the lay shaft
gearing was made, Multiple gears around the crank shaft and on the
secondary shaft could be used to provide more than one ratio in
addition to a 1:1 ratio. Alternatively, for a narrow assembly more
than one secondary shaft could be employed,
[0072] The invention is not intended to be restricted to the
details of the above-described embodiments. A myriad range of other
embodiments and variations fall within the spirit and scope of the
present disclosure.
[0073] It will be apparent to those skilled in the art that various
modifications, combinations and variations can be made in the
present invention without departing from the spirit or scope of the
invention. Specific embodiments, features and elements described
herein may be modified, and/for combined in any suitable manner.
Thus, it is intended that the present invention cover the
modifications, combinations and variations of this invention
provided they come within the scope of the appended claims and
their equivalents.
* * * * *